1. Field of the Invention
The invention relates to a method for plugging of wells for use in connection with recovery of a fluid, such as oil, gas or water.
2. Description of the Related Art
If the fluid comprises hydrocarbons, at present according to regulations plugged wells, such as offshore wells, of the above-mentioned type have to include two barriers or blocking devices which must be installed between a formation from which the hydrocarbons flow into the well and the space above the well in order to prevent hydrocarbons from leaking out of the well. For this purpose a first barrier may be employed in the form of a mechanical seal and a second barrier in the form of a mortar which is applied over the seal.
In order to apply the mortar securely, a drill string is first inserted in the well until its lower end is located near the seal. The mortar is then pumped down into the well through the drill string while the drill string is pulled up at a rate which is adapted to the rate at which the mortar is pumped down.
Even though wells are abandoned and permanently and satisfactorily secured or plugged in this manner, there may be a need for monitoring of the well, i.e. a continuous logging of well data such as pressure, temperature, electrical properties of well components, etc. Such monitoring is not possible, however, with plugging in the above-mentioned manner, since any electrical wires extending in the well from sensors which have been mounted at the bottom of the well to a logging device on the seabed at the well would have been destroyed by the drill string before or during the casting.
The object of the invention is to provide a method whereby a well of the above-mentioned type can be secured according to regulations while at the same time the well is monitored by means of sensors.
The invention relates to method for providing at least one sensor in a well at a location where a well fluid flows into the well from a subsurface formation surrounding the well, the sensor establishing a well parameter required to be monitored after the well is plugged. The method comprises the steps of connecting the sensor to the bottom of a first seal having a first connecting part on the top thereof, the sensor and the first connecting part being connected for transferring signals from the sensor to the first connecting part, placing the first seal above the location to plug the well, filling the well above the first seal with a temporarily liquid, settable sealant in an amount of the sealant so that the sealant alone plugs the well after it has set. Before the sealant has set, a first connecting device with a fourth connecting part is lowered into the sealant, the first connecting device being suspended on a cable, and the fourth connecting part is connected to the first connecting part, both the lowering and the connection of the fourth connecting part to the first connecting part being provided by the weight of the first connecting device. The cable is then connected to a logging device outside the well so that after the sealant is set, signals from the sensor are transferable to the logging device via the first connecting part of the first seal, the fourth connecting part, and the cable.